1. Field of the Invention
This invention relates to the preparation of a series of novel volatile Cu(II) metal complexes. The novel compounds, as well as some structurally similar known compounds can serve as precursors for high purity copper- or copper-containing thin-films in the absence of an external reducing reagent such as H2, and to a method for the formation of copper- or copper-containing materials on substrites, such as silicon wafers for microelectronic devices, as well as for the generation of copper-containing which temperature superconducting ceramics.
Based on the need for Cu-based electric conductors, this art has sought improvements in source materials and deposition techniques for the formation of Cu metal thin-films.
Copper thin-film materials are of great interest for use as conducting layers in integrated circuits. More specifically, such materials have been utilized for manufacturing upper level metal interconnects and for filling contact and via holes. The advantages of copper over other possible conducting materials such as aluminum include: lower resistivity (1.7 xcexcxcexa9-cm for Cu, vs. 2.7 xcexcxcexa9-cm for Al); improved electromigration resistance (up to four orders of magnitude greater than Al) and increased resistance to stress-induced voidage (due to higher melting point vs. Al). There are also several well-known advantages related to device performance such as greater speed and reduced cross tall and smaller RC time constants.
2. Description of the Prior Art
Cu(HFac)2, or copper (II) hexafluoroacetylacetonate, source reagents have been widely used to apply CVD copper to IC substrates and surfaces.1 Copper thin films have also been prepared using the related air-stable xcex2-acetoacetate and xcex2-ketoimninate Cu(II) complexes.2 The strategy for changing the ligand is either to increase the thermal stability and volatility, or to enhance the chance for selective deposition on different substrates and lower the deposition temperature of a Cu(II) complex. Upon introducing H2 as an external reducing agent into the CVD system, relatively pure copper metal has been obtained at a much lower temperature. Under these experimental conditions, the reaction is best represented by the hydrogen reduction of a Cu(II) ion, which gives rise to the formation of free xcex2-diketones as co-products:
Cu(HFac)2+H2xe2x86x92Cu+2(HFac)H
However, in the absence of an external reducing reagent, the above mentioned Cu(II) source reagents are notable for leaving large amounts of carbon, and other contaminates such as fluorine and oxygen in the deposited copper due to unwanted ligand decomposition. In addition, relatively high deposition temperatures must be used to decompose the source reagents into copper.
On the other hand, a second type or source reagent, involves the use of Cu(I) compounds to deposit copper thin film. The best known reagent of this kind is the complex (HFac)Cu(tmvs), wherein tmvs=trimethylvinylsilane,3 that has been used as an industry standard to deposit copper by CVD. Other potentially suitable Cu(I) CVD source reagents involve (HFac)CuL, wherein L=phosphine ligands such as PMe3 and PEt3, alkyne ligands such as 2-butyne, and olefin ligands such as butadiene, 1,5-cyclooctadiene, 2-methyl-1-hexene-3-yne or other volatile organosilicon compounds containing unsaturated organic groups. These reagents have been used at low temperatures to deposit the required copper metal through a thermally induced disproportionation reaction, in the absence of reducing carrier gas, such as H2. Using the Cu(J) complex (HFac)Cu(vtms) as an example, the reaction is best represented by the equation:
2(HFac)Cu(tmvs)xe2x86x92Cu+2tmvs+Cu(HFac)2
which involves the in-situ generation of deposited copper metal and a volatile Cu(II) complex Cu(HFac)2 from a thermally induced disproportionation reaction. The film resistivity obtained with this source reagent is very good, approaching the physical limit of 1.7 xcexcxcexa9-cm, i.e. the resistivity of bulk copper. This suggests the formation of high quality copper thin film materials. However, the copper(I) complex (HFac)Cu(tmvs) becomes unstable and begins to decompose above 25xc2x0 C. Thus, storage of this compound at around room temperature would lead to undesirable decomposition. In addition, the reagent (HFac)Cu(tmvs) must be converted from the liquid to the vapor state by heating during each CVD run. The aging and decomposition of (HFac)Cu(tmvs) would cause many unpredicted difficulties, such as extensive maintenance for the CVD instrument due to premature decomposition during vapor transport. In addition, this source reagent decomposes at relatively low temperature, which requires the use of lower temperatures for vapor transport and thus, lowers the precursor vapor pressure, resulting in a low rate for copper deposition, the formation of rough metal surfaces, and large variances in surface resistivity. Thus, many chemical additives and various precautions have been necessary to provide the precursors with a longer shelf life.
Accordingly, there is an urgent need for new CVD source reagents, possessing the advantages of both of the Cu(II) and Cu(I) source reagents mentioned above, namely: higher thermal and oxidative stability in air and at room temperature, lower melting point, higher vapor pressure under the designated CVD conditions;, and the capability of undergoing copper deposition in the absence of reducing carried gas H2.
Thus, it is an object of the present invention to provide such CVD source reagents and a process for using these source reagents in the formation of the copper thin-films that are highly advantageous for integration with current CVD technologies. It is another object of the present invention to provide a simplified method to generate the required source reagents, and a rationale for synthesizing such reagents.
Other objects, features, and advantages will be more fully apparent from the ensuing disclosure and appended claims.
The present invention provides a series of novel Cu(II) metal complexes of the general formula:
Cu(OCCF3R1CH2NHR2)2
wherein R1 is hydrogen, C1-C4 lower-alkyl, C1-C4 perfluorinated lower-alkyl; and R2 is C1-C6 lower-alkyl or C1-C6 lower-alkene, which may be substituted by one or more fluorine atoms, by a C1-C6 lower-alkoxy group or by a C1-C6 di-lower-alkyl amino group, provided that when R1 is CF3, R2 is other than hydrogen or methyl. Specific examples of R2 include: methyl, ethyl, allyl, n-propyl, i-propyl, 2-methoxyethyl, n-butyl, t-butyl, 3-methoxypropyl, 2,2,2-trifluoroethyl, 3,3,3,2,2-pentafluoro-n-propyl, CH2CH;NMe2, CH2CH2CH2NMe2 and CH2CH2NEt2. It will be appreciated by those skilled in the art that, having established by example that R2 may be a C1-C6 lower-alkoxy substituted alkyl, we can extrapolate R2 to a C2-C3 di-lower-alkylamino substituent, because of the similar chemical behaviour of such groups.
The copper complexes of the present invention are readily synthesized by typical synthesis techniques using conventional procedures for forming the desired complexes. The most useful synthetic method involves the direct treatment of Cu(II) halide with an excess e.g. two equivalents of an alkali metal salt of the aminoalcohol ligand HOCCF3R1CH2NHR2 at elevated temperature in the range of 40 to 80xc2x0 C., and using polar organic solvents such as THF, acetoine or diethyl ether as reaction media.